They're the only current major player, but these are good times for pinheads, as Jersey Jack is about to release his first game WOZ, and there are a few other smaller players waiting in the wings.
The others went bust cos they weren't selling enough to be profitable. Sales went down due to playstations and xboxes and pinball being noisy and needing lots of maintenance - cheaper and more profitable for a publican to get a pool table or a fruit machine.
I recommend some films on the subject, like Tilt, and Special When Lit